Abstract: Baroreceptor stimulation yields antinociceptive effects. In this study, baroreceptors were stimulated by a respiratory maneuver, with the effect of this manipulation on pain perception subsequently measured.
Methods: Thirty-eight healthy participants were instructed to inhale slowly (control condition) and to hold the air in lungs after a deep inhalation (experimental condition).
It was expected that breath-holding would increases blood pressure (BP) and thus stimulate the baroreceptors, which in turn would reduce pain perception.
Pain was induced by pressure algometry on the nail of the left-index finger, at three different pressure intensities, and quantified by visual analogue scales.
Heart rate (HR) and BP were continuously recorded.
Pain perception was lower when pain pressure was administered during the breath-holding phase versus the slow inhalation phase, regardless of the pressure intensity.
During breath-holding, a rapid increase in BP and decrease in HR were observed, demonstrating activation of the baroreceptor reflex.
Pain perception is reduced when painful stimulation is applied during breath-holding immediately following a deep inhalation.
These results suggest that a simple and easy-to-perform respiratory maneuver could be used to reduce acute pain perception.
This sounds right to me – I just hope I can remember to try it the next time I’m having an acute pain flare.
I’d love to hear from anyone who’s tried it.
The baroreceptors are pressure-stretch receptors located within the aortic arch, carotid sinus, and lungs involved in autonomic regulation and blood pressure (BP) control
Furthermore, stimulation of the baroreceptors produces a generalized inhibitory effect on the central nervous system (CNS), which included a reduction in nociception.
Electrical, pharmacological, or mechanical baroreceptor stimulation produces antinociceptive effects
Introduction [to full article]
This baroreceptor-induced CNS inhibition is one of the principal mechanisms explaining the relationship between BP and pain
The experience of pain is inversely associated with BP levels; patients with arterial hypertension experience less pain compared with normotensive individuals, and individuals with arterial hypotension have higher pain sensitivity versus normotensive subjects
Furthermore, experimentally induced increases in BP reduce pain perception
The baroreceptors are differentially stimulated during the breathing cycle. BP spontaneously oscillates in phase with respiration. Within each respiratory cycle, BP increases and decreases by between 4 and 6 mm Hg.
These BP changes result from intrapleural negative pressure during inhalation, positive intrapleural pressure during exhalation, and variations in pressure, on the abdominal viscera, as exerted by the diaphragm.
Accordingly, BP increases during the end stages of inhalation and during the onset of exhalation and decreases during the resting phase of the respiratory cycle, particularly at the onset of inhalation
Deep inhalations can increase these BP oscillations by up to 20 mm Hg . Furthermore, the responsiveness of baroreceptors (similar to other receptors such as the chemoreceptors) are modulated by respiratory CNS afferents.
Baroreceptor stimulation produces minimal heart rate (HR) responses when produced during the onset and midparts of inhalation, but produces maximal HR responses when stimulation is performed during the final stage of inhalation, and particularly during the onset of exhalation.
This effect is in turn modulated by respiratory rate; the modulation exerted by respiratory phase decreases as the respiratory rate increases, and disappears with rates of >20 breaths per minute
Breath-holding is known to produce relevant cardiovascular effects
Specially, when performed at the beginning of exhalation after a deep inhalation, this specific breath-holding is a powerful stimulus for general autonomic stimulation and specifically produces a baroreceptor-mediated large HR deceleration
This is the result of the additional rise in BP obtained from the increase in lung pressure while maintaining the inspired air within lungs.
Confirming our hypothesis, during breath-holding pain perception was lower relative to the slow inhalation condition; this effect was independent of pain pressure stimulation.
As expected, breath-holding produced an increase in BP (mediated by the positive intrachest pressure) and a fast and deep HR deceleration (mediated by the activation of the baroreceptor reflex and its efferent vagal response)
Below is a more technical physiological explanation:
During the low inhalation, SBP also increased, and HR decreased, but changes were delayed by 2–3 seconds and were reduced in magnitude.
Activation of the baroreceptors due to the increase in BP, via its connections through the CNS (nucleus of the tractus solitarius, reticular formation, thalamus, hypothalamus, amygdala, hippocampus, periaqueductal gray, insula, prefrontal, and cingulate cortex, etc.,) could produce an inhibitory effect on the CNS, with the possible related reduction in pain perception.
Low pressure baroreceptors located in the lungs, which discharged in a lineal function to tidal-volume amplitude, could also contribute to the obtained antinociceptive effect
The placebo effect, and participants’ general expectations pertaining to the effects of the two breathing conditions, might also have affected the results. However, it is improbable that, in the majority of participants, these unspecific effects would have been systematically biased toward the efficacy of the same breathing condition.
A method frequently used to assess the antinociceptive effect of baroreceptor stimulation consists of mechanical stimulation of carotid baroreceptors using neck–cuff techniques
These techniques induce neck suction (negative pressure) that stretches the baroreceptors and simulates an increase in BP. Although the resulting antinociceptive effect may depend on various factors, mechanical stimulation of the carotid baroreceptors leads to a reliable antinociceptive effect.
In conclusion, pain perception is reduced when painful stimulation is applied during breath-holding immediately following a deep inhalation.
This simple and easy-to-perform respiratory maneuver may be useful as a simple method to reduce pain in cases where an acute, short-duration pain is present or expected (e.g., medical interventions involving needling, bone manipulations, examination of injuries, etc.).